Anti-SRP myopathy, a rare form of necrotizing myopathy in an adult Nigerian female: a case report and literature review

Abstract

Anti-Signal Recognition Particle (SRP) myopathy is a rare form of Immune-Mediated Necrotizing Myopathy (IMNM). The IMNM is characterized by acute to sub-acute progressive severe symmetrical proximal myopathy with markedly elevated muscle enzymes. They have a variable response to steroids and immunosuppressive drugs. There are no sufficient data in African literature regarding this form of myopathy but rituximab has been used in refractory cases.We report a rare case of anti-SRP immune-mediated necrotizing myopathy in a 29-year-old Nigerian female with typical clinical, biochemical, and serologic features. A 29-year-old black African female presented with features of bilateral symmetrical severe progressive proximal muscle weakness of upper and lower limbs. She had no features of organspecific manifestations. Drug causes of myopathy and other connective tissue diseases were excluded. Creatine kinase was markedly elevated (18824 u/L) with positive anti-SRP antibody. She received IV methylprednisolone pulses over three days, oral prednisolone at 30mg daily, and IV rituximab weekly for initial 4 weeks and 6 monthly after unresponsiveness to azathioprine. Although initially bedridden, her symptoms improved over a few weeks of treatment as she can ambulate with support. She returned to working as a chef after 2nd course of rituximab at 6 months. Anti-SRP myopathy is a rare form of necrotizing myopathy with a variable response to steroids and immunosuppressive medications.